KR20070024856A - Image processing device and method for plasma display panel - Google Patents

Abstract

An image processing device and method for a plasma display panel are provided to enhance gray scale expression and prevent flickers generated during an error diffusion process. A reverse gamma correction unit(610) gamma-corrects external image signals by using prestored gamma data. A dither halftoning unit(631) removes false contours generated during a reverse gamma correction process by using a plurality of dither mask patterns. An error diffusion unit(632) diffuses an error component of an image signal of the previous frame to an image signal of the present frame when the difference between gray scale values of the previous frame and the present frame of the reverse gamma-corrected image signals is less than a threshold value. A subfield mapping unit(640) maps the images signals of the error diffusion unit onto a subfield mapping table.

Description

Image Processing Device and Method for Plasma Display Panel

1 illustrates a structure of a general plasma display panel.

2 is a diagram illustrating a method of implementing an image of a conventional plasma display panel.

3 is a graph comparing luminance characteristics of a plasma display panel and a cathode ray tube.

4 is a diagram illustrating inverse gamma correction in a conventional plasma display panel.

5 is a diagram illustrating a method of expressing grayscale using error diffusion and dither according to an embodiment of the present invention.

6 is a block diagram schematically illustrating an image processing apparatus of a plasma display panel according to an embodiment of the present invention.

7 is a view for explaining the operating characteristics of the dither half-toning unit according to an embodiment of the present invention.

8 is a block diagram illustrating an operating characteristic of an error diffusion unit according to an exemplary embodiment of the present invention.

9 is a schematic diagram illustrating error diffusion according to an embodiment of the present invention.

10 is a diagram illustrating a method of expressing grayscale using error diffusion and dither according to an embodiment of the present invention.

11 is a block diagram schematically illustrating an image processing apparatus of a plasma display panel according to an embodiment of the present invention.

12 is a view for explaining the operating characteristics of the dither half-toning unit according to an embodiment of the present invention.

13 is a block diagram illustrating an operating characteristic of an error diffusion unit according to an embodiment of the present invention.

14 is a schematic diagram illustrating error diffusion according to an embodiment of the present invention.

FIG. 15 is a diagram illustrating a method of expressing grayscale using first error spreading and second error spreading according to an embodiment of the present invention.

16 is a block diagram schematically illustrating an image processing apparatus of a plasma display panel according to an embodiment of the present invention.

17 is a block diagram illustrating an operating characteristic of a first error spreader according to an embodiment of the present invention.

18 is a schematic diagram illustrating a first error diffusion method according to an embodiment of the present invention.

19 is a schematic diagram illustrating a first error diffusion according to an embodiment of the present invention.

20 is a schematic diagram illustrating a first error diffusion method according to an embodiment of the present invention.

21 is a block diagram illustrating an operating characteristic of a second error spreader according to an embodiment of the present invention.

22 is a schematic diagram illustrating a second error spreading according to an embodiment of the present invention.

FIG. 23 is a diagram illustrating a method of expressing grayscale using first error diffusion and second error diffusion according to an embodiment of the present invention.

24 is a block diagram schematically illustrating an image processing apparatus of a plasma display panel according to an embodiment of the present invention.

25 is a block diagram illustrating an operating characteristic of a second error spreader according to an embodiment of the present invention.

26 is a schematic diagram illustrating a second error diffusion method according to an embodiment of the present invention.

27 is a schematic diagram illustrating a second error spreading according to an embodiment of the present invention.

28 is a schematic diagram illustrating a second error diffusion method according to an embodiment of the present invention.

29 is a block diagram illustrating an operating characteristic of a first error spreader according to an embodiment of the present invention.

30 is a schematic diagram illustrating a first error diffusion according to an embodiment of the present invention.

       (Explanation of symbols for the main parts of the drawing)

       610: reverse gamma correction unit 620: gain control unit

       630: half toning portion 631: dither half toning portion

       632: error diffusion unit 640: subfield mapping unit

       650: data alignment unit 660: data driver

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma display panel, and more particularly, to an image processing apparatus of a plasma display panel capable of ensuring reliability of gray scale representation of a plasma display panel and preventing generation of flicker.

In general, a plasma display panel (Plasma Display Panel) is a partition wall formed between the front substrate and the rear substrate to form a unit cell, each of the neon (Ne), helium (He) or a mixture of neon and helium ( The main discharge gas such as Ne + He) and an inert gas containing a small amount of xenon are filled. When discharged by a high frequency voltage, the inert gas generates vacuum ultraviolet rays and emits phosphors formed between the partition walls to realize an image. Such a plasma display panel has a spotlight as a next generation display device because of its thin and light configuration.

1 illustrates a structure of a general plasma display panel.

As shown in FIG. 1, a plasma display panel includes a front substrate in which a plurality of sustain electrode pairs formed by pairing a scan electrode 102 and a sustain electrode 103 are formed on a front glass 101, which is a display surface on which an image is displayed. The rear substrate 110 having the plurality of address electrodes 113 arranged to intersect the plurality of sustain electrode pairs on the back glass 111 forming the back surface 100 and the rear surface is coupled in parallel with a predetermined distance therebetween. .

The front substrate 100 may include a scan electrode 102 and a sustain electrode 103, that is, a transparent electrode a made of a transparent indium thin oxide (ITO) material for mutual discharge in one discharge cell and maintaining light emission of the cell. It is covered by one or more dielectric layers 104 which limit the discharge current of the scan electrode and the sustain electrode 103 provided with the bus electrode b made of a metal material and insulate the electrode pairs. A protective layer 105 in which magnesium oxide (MgO) is deposited is formed on the entire surface of the dielectric layer 104 to facilitate discharge conditions.

The rear substrate 110 is arranged in such a manner that a plurality of discharge spaces, that is, barrier ribs 112 of a stripe type (or well type) for forming discharge cells are maintained in parallel. In addition, a plurality of address electrodes 113 which perform address discharge to generate vacuum ultraviolet rays are arranged in parallel with the partition wall 112. On the upper side of the rear substrate 110, R, G, and B phosphors 114 which emit visible light for image display during address discharge are coated. A dielectric layer 115 is formed between the address electrode 113 and the phosphor 114 to protect the address electrode 113.

2 is a diagram illustrating a method of implementing an image of a conventional plasma display panel.

As shown in FIG. 2, the plasma display panel divides one frame period into a plurality of subfields having different discharge times, and emits the plasma display panel in a subfield period corresponding to a gray value of an input image signal. An image is implemented.

Each subfield is divided into a reset period for uniformly generating a discharge, an address period for selecting a discharge cell, and a sustain period for implementing gray scale according to the number of discharges. For example, when the image is to be displayed with 256 gray levels, the frame period (16.67 ms) corresponding to 1/60 second is divided into eight subfields.

In addition, each of the eight subfields is divided into a reset period, an address period, and a sustain period. Here, the sustain period is increased at the ratio of 2 ⁿ (n = 0,1,2,3,4,5,6,7) in each subfield. As described above, since the sustain period is changed in each subfield, gray levels of an image can be realized.

3 is a graph comparing luminance characteristics of a plasma display panel and a cathode ray tube.

As shown in FIG. 3, a cathode-ray tube and a liquid crystal display display a desired gray scale by controlling the displayed light in an analog manner with respect to an input video signal. It has a luminance characteristic of. In contrast, since the plasma display panel modulates the number of light pulses by using a matrix array of discharge cells that can be turned on / off, the plasma display panel has a linear luminance characteristic.

The gray scale expression method of the plasma display panel is called a PWM (pulse width modulation) method. The luminance of the plasma display panel changes linearly with the number of pulses, but since the degree of perception of our vision is nonlinear, noise is generated when the gray scale is expressed in the low gray scale region. Therefore, in order to solve the above problem, the plasma display panel inversely gamma corrects the input image signal data as shown in FIG. 4.

4 is a graph illustrating inverse gamma correction in a conventional plasma display panel.

In Fig. 4, the target luminance is an ideal inverse gamma result to be corrected, and the actual luminance is a measured luminance value as a result after inverse gamma correction, and the plasma display panel luminance is a luminance value measured in the absence of inverse gamma correction. 3 or less is shown.

As shown in FIG. 4, the target luminance is expressed as luminance values having different gray level values of 61 steps from 0 to 60, respectively. In contrast, the actual luminance is expressed by only eight luminance values of 61 gray levels up to 0-60. Therefore, when the inverse gamma correction is performed in the plasma display panel, sufficient gray scale expression cannot be expressed in a dark area, resulting in a contour noise in which images are aggregated.

In order to express the insufficient gray level of the plasma display panel, a half tone method such as a dithering method and an error diffusion method is conventionally used.

However, the above-described methods have a problem in that flicker occurs on the screen if a screen having the same gradation appears on the entire screen or the error accumulated at the time when the still image appears is the same value for the entire screen.

Accordingly, an object of the present invention is to provide an image processing apparatus of a plasma display panel that can ensure reliability of gray scale expression and prevent generation of flicker.

Technical problems to be achieved by the present invention are not limited to the above-mentioned technical problems, and other technical problems not mentioned above will be clearly understood by those skilled in the art from the following description. Could be.

The image processing apparatus of the plasma display panel according to an embodiment of the present invention for achieving the above technical problem is generated by the inverse gamma correction unit, the inverse gamma correction step for gamma correction of the image signal applied from the outside with pre-stored gamma data Dither half-toning unit for removing pseudo contours using a plurality of dither mask patterns for the least significant digit from the decimal point to a predetermined bit, and the previous frame of the video signal inverse-gamma corrected to the decimal point bits other than the predetermined bit (N-1 When the difference between the gray level value of the current frame N and the current frame N is less than or equal to a predetermined threshold value, an error spreader and an image signal input from an error diffuser and an error diffuser for diffusing an error component of the video signal of the previous frame into the video signal of the current frame Subfield mapping unit for mapping to the subfield mapping table.

In addition, it is preferable that the predetermined bit is 2-5 bits among the bits below the decimal point.

In addition, the error diffusion unit includes a frame memory unit for storing the inverse gamma corrected image signal in units of frames, and an error diffusion determination method for determining an error diffusion by comparing a difference between grayscale values of a previous frame and a current frame of the image signal with a predetermined threshold value. And an error diffusion unit for diffusing an error component of the image signal according to the information input from the unit and the error diffusion determination unit.

In addition, the predetermined threshold is preferably 1.

The image processing apparatus of the plasma display panel according to an embodiment of the present invention for achieving the above technical problem is an inverse gamma correction unit for gamma correction of the image signal applied from the outside with pre-stored gamma data, When the difference between the gradation values of the previous frame N-1 and the current frame N is less than or equal to a predetermined threshold value, the error component of the video signal of the previous frame is changed from the least significant digit below the decimal point to the predetermined bit. An image signal input from a dither half toning unit and a dither half toning unit which removes an error diffusion unit for diffusing into the second gamma correction step and a pseudo contour generated in the inverse gamma correction step by using a plurality of dither mask patterns for a decimal point bit other than a predetermined bit. It includes a subfield mapping unit for mapping to a subfield mapping table.

In addition, it is preferable that the predetermined bit is 2-5 bits among the bits below the decimal point.

In addition, the error diffusion unit includes a frame memory unit for storing the inverse gamma corrected image signal in units of frames, and an error diffusion unit determining whether the error is spread by comparing a difference between the gray level values of the previous frame and the current frame of the image signal with a predetermined threshold value. And an error diffusion unit for diffusing an error component of the image signal according to the information input from the determination unit and the error diffusion determination unit.

In addition, the predetermined threshold is preferably 1.

The image processing apparatus of the plasma display panel according to an embodiment of the present invention for achieving the above technical problem is an inverse gamma correction unit for performing gamma correction of the image signal applied from the outside with pre-stored gamma data, A first error diffusion unit for diffusing an error component of an image signal of an adjacent pixel from a least significant digit to a predetermined bit below the decimal point, and a previous frame of the image signal inverse gamma corrected to a decimal point other than the predetermined bit (N-1) ) Is input from the second error spreader and the second error spreader to spread the error component of the video signal of the previous frame to the video signal of the current frame when the difference between the gray level value of the current frame N is equal to or less than a predetermined threshold value. And a subfield mapping unit for mapping the video signal to the subfield mapping table.

In addition, it is preferable that the predetermined bit is 2-5 bits among the bits below the decimal point.

In addition, the first error diffusion unit compares the difference between the gray level values between the image signal stored in the line memory unit and the image signal stored in the line memory unit, and stores the inverse gamma corrected image signal in line units. And a first error diffusion determiner for selecting an image signal of a pixel having a difference in gray level value equal to or less than a predetermined threshold value, and a first error diffusion performer for performing error component diffusion of the image signal of the selected pixel.

In addition, the predetermined threshold is preferably 1.

In addition, it is preferable that the direction of the first error diffusion is reversed for each line.

The second error diffusion unit may further include a frame memory unit configured to store the inverse gamma corrected image signal in units of frames, and determine whether the error is spread by comparing a difference between the gray level values of the previous frame and the current frame of the image signal with the predetermined threshold value. And a second error diffusion unit for diffusing an error component of the image signal according to the information input from the second error diffusion determination unit and the second error diffusion determination unit.

In addition, the predetermined threshold is preferably 1.

The image processing apparatus of the plasma display panel according to an embodiment of the present invention for achieving the above technical problem is an inverse gamma correction unit for gamma correction of the image signal applied from the outside with pre-stored gamma data, When the difference between the gradation values of the previous frame N-1 and the current frame N is less than or equal to a predetermined threshold value, the error component of the video signal of the previous frame is changed from the least significant digit below the decimal point to the predetermined bit. Input from a second error diffuser and a second error diffuser for diffusing the error components of the video signal of adjacent pixels for bits below the decimal point other than the predetermined bits among the reverse gamma corrected image signals; And a subfield mapping unit for mapping the video signal to a subfield mapping table.

In addition, it is preferable that the predetermined bit is 2-5 bits among the bits below the decimal point.

The second error diffusion unit compares the difference between the gray level values of the image signal stored in the line memory unit and the image signal stored in the line memory unit, and stores the inverse gamma corrected image signal in units of lines. And a second error diffusion determiner that selects an image signal of a pixel having a difference in gray level value equal to or less than a predetermined threshold value, and a second error diffuser that performs error component diffusion of the image signal of the selected pixel.

In addition, the predetermined threshold is preferably 1.

In addition, it is preferable that the second error diffusion is reversed in direction for each line.

The first error diffusion unit may include a frame memory unit configured to store the inverse gamma corrected image signal in units of frames, and determine whether the error is spread by comparing a difference between the gray level values of the previous frame and the current frame of the image signal with a predetermined threshold value. The first error spreader includes an error component of the video signal according to information input from the first error spreader and the first error spreader.

In addition, the predetermined threshold is preferably 1.

The image processing method of the plasma display panel according to an embodiment of the present invention for achieving the another technical problem is generated in the inverse gamma correction step, the inverse gamma correction step to gamma correct the image signal applied from the outside with pre-stored gamma data A dither halftoning step of removing pseudo contours using a plurality of dither mask patterns for the least significant digit from the decimal point to a predetermined bit, and the previous frame of the image signal inversely gamma corrected for bits other than the predetermined bit. 1) and an error diffusion step of diffusing an error component of the image signal of the previous frame into the image signal of the current frame when the difference between the gradation values of the current frame N is less than or equal to a predetermined threshold value and the image input after the error diffusion. A subfield mapping step of mapping the signal to a subfield mapping table.

The image processing method of the plasma display panel according to an embodiment of the present invention for achieving the another technical problem is an inverse gamma correction step of gamma correction of the image signal applied from the outside with pre-stored gamma data, the reverse gamma corrected image signal When the difference between the gradation values of the previous frame N-1 and the current frame N is less than or equal to a predetermined threshold value, the error component of the video signal of the previous frame is calculated from the least significant digit from the decimal point to the predetermined bit. Input after a dither halftoning step and a dither halftoning step of removing pseudo contours generated in an error diffusion step and an inverse gamma correction step for diffusing a signal using a plurality of dither mask patterns for a decimal point bit other than the predetermined bit. And a subfield mapping step of mapping the video signal to the subfield mapping table.

The image processing method of the plasma display panel according to an embodiment of the present invention for achieving the another technical problem is a reverse gamma correction step, gamma correction step of the image signal applied from the outside with pre-stored gamma data, the reverse gamma corrected image signal A first error diffusion step of diffusing an error component of an image signal of an adjacent pixel from a least significant digit of a decimal point to a predetermined bit; a previous frame (N) of the inverse gamma corrected image signal for a decimal point other than a predetermined bit A second error diffusion step and a second error diffusion step of diffusing the error component of the image signal of the previous frame to the image signal of the current frame when the difference between the gray level value of the negative frame 1 and the current frame N is less than or equal to a predetermined threshold; And a subfield mapping step of mapping an input video signal to a subfield mapping table.

The image processing method of the plasma display panel according to an embodiment of the present invention for achieving the another technical problem is an inverse gamma correction step of gamma correction of the image signal applied from the outside with pre-stored gamma data, the reverse gamma corrected image signal When the difference between the gradation values of the previous frame N-1 and the current frame N is less than or equal to a predetermined threshold value, the error component of the video signal of the previous frame is calculated from the least significant digit from the decimal point to the predetermined bit. Input after the first error diffusion step of diffusing the signal, the second error diffusion step of diffusing the error component of the video signal of the adjacent pixel with respect to the decimal point bits other than the predetermined bit of the inverse gamma corrected image signal, and the second error diffusion step. And a subfield mapping step of mapping the video signal to a subfield mapping table.

Specific details of other embodiments are included in the detailed description and the drawings. Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. Like reference numerals refer to like elements throughout.

 <First Embodiment>

5 is a diagram illustrating a method of expressing grayscale using error diffusion and dither according to an embodiment of the present invention. As shown in Fig. 5, a value above the decimal point of the gray level is called a real gray level, and a method of error diffusion or dither is used using a value below the decimal point. Dither is used for the least significant digits after the decimal point and the predetermined bit, and a method in which error diffusion is used for the decimal point bits other than the predetermined bits described above is used. Herein, the predetermined bit is preferably 2 to 5 bits among the bits below the decimal point. In more detail, it is preferable that it is 4 bits of the decimal point bits. First, a carry is generated in the dither bits (4 to 7 bits) and transferred to the error diffusion bits (1 to 3 bits), and a carry is generated in the error diffusion bits and transferred to the real gradation bits. . As a result, various gradation expressions are possible using only real gradation values. Here, the carry means a lift. Herein, the predetermined bits are shown as four bits, which are arbitrarily written to facilitate the description of the present invention, and are not limited thereto.

Here, an image processing apparatus of a plasma display panel that embodies gradation representation using error diffusion and dither according to an embodiment of the present invention will be described with reference to FIG. 6.

6 is a block diagram schematically illustrating an image processing apparatus of a plasma display panel according to an embodiment of the present invention.

As illustrated in FIG. 6, an image processing apparatus of a plasma display panel according to an exemplary embodiment of the present invention may include an inverse gamma correction unit 610, a gain control unit 620, a dither half toning unit 631, and an error diffusion unit ( 632, a subfield mapping unit 640, a data alignment unit 650, and a data driver 660.

The inverse gamma correction unit 610 gamma-corrects an input image signal through pre-stored gamma data, and linearly converts a displayed luminance value according to a gray value of the input image signal.

The gain controller 620 may be adjusted by a user or a set maker with respect to the red, green, and blue image signals corrected by the inverse gamma correction unit 610. Adjust the gain by red, green and blue by multiplying the gain values. In this case, the gain controller 620 may set a color temperature desired by the user or the set maker. In one embodiment of the present invention further includes a gain control unit 620 for performing such a function.

The dither half toning unit 631 uses a plurality of dither mask patterns for the pseudo contour generated by the inverse gamma correction unit 610 to the image signal input from the gain control unit 620 from the least significant digit below the decimal point to a predetermined bit. Remove The description thereof will be described later in more detail.

The error diffusion unit 632 may improve the gradation expression power by finely adjusting the luminance value displayed according to the gradation value by diffusing an error component with respect to the image signal input from the gain control unit 620.

In the error diffusion unit 632 according to an embodiment of the present invention, in performing error diffusion, a previous frame (N-1) and a current frame (N-1) of an inverse gamma corrected image with respect to bits below the decimal point other than a predetermined bit may be used. When the difference between the gray level values of N) is less than or equal to a predetermined threshold value, temporal error spreading is performed to spread the error component of the video signal of the previous frame to the video signal of the current frame. The description thereof will be described later in more detail.

The subfield mapping unit 640 maps the image signal input from the error diffusion unit 632 to a preset subfield mapping table.

The data sorter 650 sorts the spatially sorted subfield mapping data input from the subfield mapper 640 into temporal data.

The data driver 660 receives the data aligned in time by the data aligning unit 650 and supplies an address driving pulse to an address electrode (not shown) of the plasma display panel, thereby realizing an image of the plasma display panel. This half-toning method is defined as 3D halftoning.

Here, the dither half toning unit according to an embodiment of the present invention will be described in detail with reference to FIG. 7.

7 is a view for explaining the operating characteristics of the dither half-toning unit according to an embodiment of the present invention.

As illustrated in FIG. 7, the dither half toning step 631 is performed by comparing a gray level value from the least significant digit to the predetermined bit of each pixel to a specific threshold value of the dither mask 710. It is a step of determining whether a carry has occurred. That is, it is a step of increasing the gray scale expression power which is insufficient by turning on the pixel on which the spot has occurred and off on the pixel which does not.

The dither mask is used to determine the specific threshold described above. When the dither mask uses one pattern having the same gray scale value every frame, the dither noise of the pattern is noticeable to a human. Therefore, the dither mask pattern is applied differently every frame. Although the number of mask patterns can be further increased, it is appropriate to employ 4 to 8 patterns per same gradation for the number of dither mask patterns.

In addition, the error diffusion unit according to an embodiment of the present invention will be described in detail with reference to FIG. 8.

8 is a block diagram illustrating an operating characteristic of an error diffusion unit according to an exemplary embodiment of the present invention.

As shown in FIG. 8, the error diffusion unit 800 according to an embodiment of the present invention includes a frame memory unit 810, an error diffusion determination unit 820, and an error diffusion execution unit 830.

The frame memory unit 810 stores the inverse gamma corrected image signal in units of lines. In addition, the frame memory unit 810 stores the gray level value of the image signal in which the error diffusion is performed, and repeats it for every pixel. In an exemplary embodiment of the present invention, the frame memory unit 810 is included in the error diffusion unit 800, but generally, the frame memory unit included in the plasma display panel may be used. That is, the frame memory unit may be located outside the error diffusion unit.

The error diffusion determination unit 820 obtains a difference between gray level values of the image signal of the previous frame N-1 input from the frame memory unit 810 and the image signal of the current frame N input after the inverse gamma correction. Thereafter, the difference value of the grayscale value and a predetermined threshold value are compared to determine whether the error is spread.

The error spreading unit 830 spreads the error component of the image signal in time according to the information input from the error diffusion determining unit 820.

In an embodiment of the present invention, the gray level values of the image signals of the previous frame and the current frame are compared with each pixel, and error diffusion is performed.

At this time, error components of the video signal of the error-spread current frame are accumulated. That is, the error component of the previous frame N-1 is received from the current frame N to affect the current frame, and the error of the current frame is accumulated. By accumulating the error of the current frame affects the next frame (N + 1) again, it is possible to suppress the loss of the gradation representation due to the quantization of the image signal. Here, the difference between the gray level value of each of the previous frame, the current frame, the current frame, and the next frame must satisfy a predetermined threshold value or less.

When the difference in the gray value of the image signal according to the embodiment of the present invention exceeds a predetermined threshold value, the accumulated error component is erased. That is, since the human eye accumulates light in time and feels its brightness, when the gray value difference of the image signal exceeds a predetermined threshold value, spreading an error component adversely affects an image to be realized. Therefore, in an exemplary embodiment of the present invention, when the gray value difference of the image signal exceeds a predetermined threshold value, the accumulated error component is erased so that the gray value of the frame where the gray value difference occurs does not be affected.

At this time, the predetermined threshold value according to an embodiment of the present invention is characterized in that 1. Although the predetermined threshold value is set to 1 according to an embodiment of the present invention, it may be arbitrarily set according to the image to be implemented. After inverse gamma correction, the video signal has a gray value having an integer part and a fractional part. Accordingly, the image signal having a difference in gradation value of 1 or more does not perform error diffusion by a threshold value, and the image signal having a difference in gradation value of 1 or less performs error diffusion by a threshold value.

As a result, it is possible to exclude a video signal of a frame having an adverse effect due to the error spreading, to perform a more reliable error spreading, and to prevent the occurrence of flicker when only the temporal error spreading is performed.

The image processing method of the plasma display panel according to the exemplary embodiment of the present invention includes the following steps.

First, gamma correction is performed on an externally applied video signal with gamma data stored in advance.

Thereafter, the pseudo contour generated in the inverse gamma correction step is removed using a plurality of dither mask patterns for the least significant digit from the decimal point to a predetermined bit.

Subsequently, when the difference between the grayscale values of the previous frame N-1 and the current frame N of the reverse gamma-corrected video signal with respect to bits below the decimal point other than the predetermined bit is less than or equal to a predetermined threshold, the error of the video signal of the previous frame. The component is spread over the video signal of the current frame.

Thereafter, an image signal input after error diffusion is mapped to a subfield mapping table.

At this time, the error diffusion method is performed according to the following steps.

First, the inverse gamma corrected image signal is stored in units of frames.

Thereafter, the difference between the gray level values of the previous frame and the current frame of the image signal is compared with a predetermined threshold value to determine whether the error is spread.

Then, the error component of the video signal is spread in time according to the information input by the error diffusion determination.

At this time, error components of the video signal of the error-spread current frame are accumulated. In addition, when the gray value difference of the video signal exceeds a predetermined threshold value, the accumulated error component is erased and initialized. The predetermined threshold value is one.

9 is a schematic diagram illustrating an error diffusion method according to an embodiment of the present invention. The operation of the block of FIG. 9 may be represented by Equations 1, 2, and 3 below.

[Equation 1]

[Equation 2]

[Equation 3]

9 and the parameters of Equations 1, 2 and 3 are defined as follows.

D is an error diffusion determining block that determines whether or not an error is spread.

Q is a quantization block that quantizes the inverse gamma corrected video signal.

Z is an error component delay block that delays the error components in time.

n represents the current frame.

n-1 represents the previous frame.

F (i, j) represents the input image signal after inverse gamma correction. In this case, i and j are coordinates representing pixel positions of the video signal.

B (i, j) is a video signal quantized by a Q block.

E (i, j) is the temporal error component of the video signal. That is, the quantization error component generated in the previous frame.

f (i, j) is the error spread video signal. That is, f (i, j) is an image signal obtained by accumulating an error component delayed by one frame through Z blocks in the previous frame to F (i, j) in the current frame.

Referring to FIG. 9 and Equation 1, Equation 2, and Equation 3, first, the error diffusion is performed by comparing the difference of gray values with a predetermined threshold value and determining whether the error is spread. In FIG. 9, it is determined whether an error spreads in the D block.

At this time, in one embodiment of the present invention, when the difference between the grayscale value of the previous frame and the current frame is less than or equal to a predetermined threshold value, error diffusion is performed so that the f (i, j) value has the value shown in Equation (2).

In addition, when the difference between the gray level value of the previous frame and the current frame exceeds a predetermined threshold value, the error component is erased and initialized, so that the value of f (i, j) output from the D block is F (i , j).

As described above, gray scales are expressed by using dither and error diffusion at the same time, thereby increasing gray scale expressing power and preventing flicker generated during error diffusion.

 Second Embodiment

10 is a diagram illustrating a method of expressing grayscale using error diffusion and dither according to an embodiment of the present invention. As shown in Fig. 10, a value greater than or equal to the decimal point of the gray level is called a real gray level, and a method of error diffusion or dither is used using a value less than or equal to the decimal point. Error diffusion is used for the least significant digits after the decimal point to the predetermined bit, and a dither is used for the decimal point bits other than the predetermined bits described above. Herein, the predetermined bit is preferably 2 to 5 bits among the bits below the decimal point. In more detail, it is preferable that it is 4 bits of the decimal point bits. First, a carry is generated in the error diffusion bits (4 to 7 bits) and transferred to the dither bits (1 to 3 bits), and a carry is generated in the dither bits and transferred to the real gradation bits. As a result, various gradation expressions are possible using only real gradation values. Here, the carry means a lift. Herein, the predetermined bits are shown as four bits, which are arbitrarily written to facilitate the description of the present invention, and are not limited thereto.

Here, an image processing apparatus of a plasma display panel that embodies gradation representation using error diffusion and dither according to an embodiment of the present invention will be described with reference to FIG. 11.

11 is a block diagram schematically illustrating an image processing apparatus of a plasma display panel according to an embodiment of the present invention.

As illustrated in FIG. 11, an image processing apparatus of a plasma display panel according to an exemplary embodiment of the present invention may include an inverse gamma correction unit 1110, a gain control unit 1120, an error diffusion unit 1131, and a dither half toning unit ( 1132, a subfield mapping unit 1140, a data alignment unit 1150, and a data driver 1160.

The inverse gamma correction unit 1110 gamma-corrects an input image signal through pre-stored gamma data, and linearly converts a displayed luminance value according to a gray value of the input image signal.

The gain controller 1120 may be adjusted by a user or a set maker with respect to the red, green, and blue image signals corrected by the inverse gamma correction unit 1110. Adjust the gain by red, green and blue by multiplying the gain values. In this case, the gain controller 1120 may set a color temperature desired by the user or the set maker. In one embodiment of the present invention further includes a gain control unit 620 for performing such a function.

The error diffusion unit 1131 may improve the gradation expression power by finely adjusting the luminance value displayed according to the gradation value by diffusing an error component with respect to the image signal input from the gain control unit 1120.

In the error diffusion unit 1131 according to an embodiment of the present invention, in order to perform error diffusion, the previous frame of the video signal that has been inverse gamma corrected for the least significant digits after the decimal point to a predetermined bit (4 to 7 bits) When the difference between the gray level value of N-1) and the current frame N is less than or equal to a predetermined threshold value, temporal error spreading is performed to spread the error component of the image signal of the previous frame to the image signal of the current frame. The description thereof will be described later in more detail.

The dither half toning unit 1132 may include a plurality of sub-bits (1 to 3 bits) other than the predetermined bits for the pseudo contour generated by the inverse gamma correction unit 1110 to the image signal input from the gain control unit 1120. Remove using dither mask pattern. The description thereof will be described later in more detail.

The subfield mapping unit 1140 maps an image signal input from the dither half toning unit 1132 to a preset subfield mapping table.

The data arranging unit 1150 sorts the spatially sorted subfield mapping data input from the subfield mapping unit 1140 into temporal data.

The data driver 1160 receives data temporally aligned by the data aligner 1150 and supplies an address driving pulse to an address electrode (not shown) of the plasma display panel, thereby implementing an image of the plasma display panel. This half toning is defined as 3D halftoning.

Here, the error diffusion unit according to an embodiment of the present invention will be described in detail with reference to FIG. 13.

13 is a block diagram illustrating an operation characteristic of an error diffusion unit according to an exemplary embodiment of the present invention.

As shown in FIG. 13, the error diffusion unit 1300 according to an embodiment of the present invention includes a frame memory unit 1310, an error diffusion determination unit 1320, and an error diffusion execution unit 1330.

The frame memory unit 1310 stores the inverse gamma corrected image signal in line units. In addition, the frame memory unit 1310 stores the gray scale value of the image signal in which the error diffusion is performed, and repeats it every pixel. In one embodiment of the present invention, the frame memory unit 1310 is included in the error diffusion unit 1300, but generally, the frame memory unit included in the plasma display panel may be used. That is, the frame memory unit may be located outside the error diffusion unit.

The error diffusion determination unit 1320 obtains a difference between gray level values of the image signal of the previous frame N-1 input from the frame memory unit 1310 and the image signal of the current frame N input after the inverse gamma correction. Thereafter, the difference value of the grayscale value and a predetermined threshold value are compared to determine whether the error is spread.

The error spreading unit 1330 spreads the error components of the image signal in time according to the information input from the error spreading determination unit 1320. In an embodiment of the present invention, the image of the previous frame and the current frame in pixel units, respectively. The gray level values of the signals are compared, and error diffusion is performed.

At this time, error components of the video signal of the error-spread current frame are accumulated. That is, the error component of the previous frame N-1 is received from the current frame N to affect the current frame, and the error of the current frame is accumulated. By accumulating the error of the current frame affects the next frame (N + 1) again, it is possible to suppress the loss of the gradation representation due to the quantization of the image signal. Here, the difference between the gray level value of each of the previous frame, the current frame, the current frame, and the next frame must satisfy a predetermined threshold value or less.

When the difference in the gray value of the image signal according to the embodiment of the present invention exceeds a predetermined threshold value, the accumulated error component is erased. That is, since the human eye accumulates light in time and feels its brightness, when the gray value difference of the image signal exceeds a predetermined threshold value, spreading an error component adversely affects an image to be realized. Therefore, in an exemplary embodiment of the present invention, when the gray value difference of the video signal exceeds a predetermined threshold value, the accumulated error component is erased so that the gray value of the frame in which the gray value difference occurs is not affected.

At this time, the predetermined threshold value according to an embodiment of the present invention is characterized in that 1. Although the predetermined threshold value is set to 1 according to an embodiment of the present invention, it may be arbitrarily set according to the image to be implemented. After inverse gamma correction, the video signal has a gray value having an integer part and a fractional part. Accordingly, the image signal having a difference in gradation value of 1 or more does not perform error diffusion by a threshold value, and the image signal having a difference in gradation value of 1 or less performs error diffusion by a threshold value.

In addition, the dither half toning unit according to an embodiment of the present invention will be described in detail with reference to FIG. 12.

12 is a view for explaining the operating characteristics of the dither half-toning unit according to an embodiment of the present invention.

As shown in FIG. 12, the dither half-toning step 1132 includes a gray level value of the decimal point bits (1 to 3 bits) other than the above-described predetermined bits of each pixel. It is a step of determining whether a carry occurs by comparing with a threshold value. That is, it is a step of increasing the gray scale expression power which is insufficient by turning on the pixel on which the spot has occurred and off on the pixel which does not.

The dither mask is used to determine the specific threshold described above. When the dither mask uses one pattern having the same gray scale value every frame, the dither noise of the pattern is noticeable to a human. Therefore, the dither mask pattern is applied differently every frame. Although the number of mask patterns can be further increased, it is appropriate to employ 4 to 8 patterns per same gradation for the number of dither mask patterns.

Here, in the above-described second embodiment, error diffusion is first performed on the least significant digit from the decimal point to the predetermined bit, and the dither carry is performed in real gradation by performing dither half-toning on the decimal point other than the predetermined bit. It can be seen that it differs from the first embodiment in terms of transmission.

As described above, by performing the half-toning step as in the second embodiment, it is possible to exclude the image signal of the frame adversely affected by the error spreading, to perform more reliable error spreading, and to perform flicker than the temporal error spreading. It can prevent occurrence.

The image processing method of the plasma display panel according to the exemplary embodiment of the present invention includes the following steps.

First, inverse gamma correction is performed to gamma-correct an image signal applied from the outside to pre-stored gamma data.

Subsequently, when the difference between the grayscale values of the previous frame N-1 and the current frame N of the inverse gamma corrected video signal is less than or equal to a predetermined threshold value, the image of the previous frame with respect to the least significant digit from the decimal point to a predetermined bit. The error component of the signal is spread over the video signal of the current frame.

Subsequently, the pseudo contour generated in the inverse gamma correction step is removed using a plurality of dither mask patterns for bits below the decimal point other than the predetermined bits.

Thereafter, an image signal input after the dither halftoning step is mapped to a subfield mapping table.

At this time, the error diffusion method is performed according to the following steps.

First, the inverse gamma corrected image signal is stored in units of frames.

Thereafter, the difference between the gray level values of the previous frame and the current frame of the image signal is compared with a predetermined threshold value to determine whether the error is spread.

Then, the error component of the video signal is spread in time according to the information input by the error diffusion determination.

At this time, error components of the video signal of the error-spread current frame are accumulated. In addition, when the gray value difference of the video signal exceeds a predetermined threshold value, the accumulated error component is erased and initialized. The predetermined threshold value is one.

14 is a schematic diagram illustrating an error diffusion method according to an embodiment of the present invention. The operation of the block of FIG. 14 may be expressed by Equations 1, 2, and 3 below.

[Equation 1]

[Equation 2]

[Equation 3]

14 and the parameters of Equations 1, 2 and 3 are defined as follows.

D is an error diffusion determining block that determines whether or not an error is spread.

Q is a quantization block that quantizes the inverse gamma corrected video signal.

Z is an error component delay block that delays the error components in time.

n represents the current frame.

n-1 represents the previous frame.

F (i, j) represents the input image signal after inverse gamma correction. In this case, i and j are coordinates representing pixel positions of the video signal.

B (i, j) is a video signal quantized by a Q block.

E (i, j) is the temporal error component of the video signal. That is, the quantization error component generated in the previous frame.

f (i, j) is the error spread video signal. That is, f (i, j) is an image signal obtained by accumulating an error component delayed by one frame through Z blocks in the previous frame to F (i, j) in the current frame.

Referring to FIG. 14 and Equation 1, Equation 2, and Equation 3, first, the error diffusion is performed by comparing the difference in gray values with a predetermined threshold value and determining whether the error is spread. In FIG. 9, it is determined whether an error spreads in the D block.

At this time, in one embodiment of the present invention, when the difference between the grayscale value of the previous frame and the current frame is less than or equal to a predetermined threshold value, error diffusion is performed so that the f (i, j) value has the value shown in Equation (2).

In addition, when the difference between the gray level value of the previous frame and the current frame exceeds a predetermined threshold value, the error component is erased and initialized, so that the value of f (i, j) output from the D block is F (i , j).

As described above, gray scales are expressed by using dither and error diffusion at the same time, thereby increasing gray scale expressing power and preventing flicker generated during error diffusion.

Third Embodiment

FIG. 15 is a diagram illustrating a method of expressing grayscale using first error spreading and second error spreading according to an embodiment of the present invention. As shown in FIG. 15, a value above the decimal point of the gray scale is called a real gray scale, and temporal error diffusion and spatial error diffusion are used using a value below the decimal point. The first error spreading is spatially used for the least significant digits below the decimal point and the predetermined bit, and the second error spreading is used temporally for the decimal point bits other than the predetermined bits. Herein, the predetermined bit is preferably 2 to 5 bits among the bits below the decimal point. In more detail, it is preferable that it is 4 bits of the decimal point bits. First, a carry occurs in the first error spreading bits (4 to 7 bits) and is transferred to the second error spreading bits (1 to 3 bits), and a carry occurs in the second error spreading bits to generate a real. Passed as (real) gradation bits. As a result, various gradation expressions are possible using only real gradation values. Here, the carry means a lift. Herein, the predetermined bits are shown as four bits, which are arbitrarily written to facilitate the description of the present invention, and are not limited thereto.

Here, an image processing apparatus of a plasma display panel that embodies gradation representation using the first error diffusion and the second error diffusion according to an embodiment of the present invention will be described with reference to FIG. 16.

16 is a block diagram schematically illustrating an image processing apparatus of a plasma display panel according to an embodiment of the present invention.

As illustrated in FIG. 16, an image processing apparatus of a plasma display panel according to an exemplary embodiment of the present invention may include an inverse gamma correction unit 1610, a gain control unit 1620, a first error diffusion unit 1631, and a second error. The diffusion unit 1632, the subfield mapping unit 1640, the data alignment unit 1650, and the data driver 1660 are provided.

The inverse gamma correction unit 1610 gamma-corrects an input image signal through pre-stored gamma data, and linearly converts a displayed luminance value according to a gray value of the input image signal.

The gain controller 1620 may be adjusted by a user or a set maker with respect to the red, green, and blue image signals corrected by the inverse gamma correction unit 1610. Adjust the gain by red, green and blue by multiplying the gain values. In this case, the gain controller 1620 may set the color temperature desired by the user or the set maker. In one embodiment of the present invention further includes a gain control unit 1620 performing such a function.

The first error diffusion unit 1631 spatially diffuses an error component to adjacent pixels with respect to an image signal input from the gain control unit 1620 for the least significant digit from the decimal point to a predetermined bit, thereby displaying luminance according to the grayscale value. By finely adjusting the value, the gradation power can be improved. In addition, in performing the error diffusion, the first error diffusion unit 1631 according to an embodiment of the present invention may determine that the difference between the grayscale values and the inverse gamma corrected image signal is less than or equal to a predetermined threshold. The error component of the video signal is spread. That is, it is possible to determine whether or not the error diffusion is performed according to the grayscale value of the adjacent pixel, and selectively perform the error diffusion. The description thereof will be described later in more detail.

The second error diffusion unit 1632 may diffuse the error component in time with respect to the image signal input from the gain control unit 1620, thereby finely adjusting the luminance value displayed according to the gray scale value to improve the gray scale expression power.

In performing the error diffusion, the second error spreader 1632 according to an embodiment of the present invention includes the previous frame (N-1) and the current frame of the video signal that has been inverse gamma corrected for bits below the decimal point other than a predetermined bit. When the gray value difference of the frame N is less than or equal to a predetermined threshold, temporal error spreading is performed to spread the error component of the image signal of the previous frame to the image signal of the current frame. The description thereof will be described later in more detail.

The subfield mapping unit 1640 maps the image signal input from the second error diffusion unit 1632 to a preset subfield mapping table.

The data arranging unit 1650 sorts the spatially aligned subfield mapping data input from the subfield mapping unit 1640 into temporal data.

The data driver 1660 receives the time-aligned data by the data aligning unit 1650 and supplies an address driving pulse to an address electrode (not shown) of the plasma display panel, thereby realizing an image of the plasma display panel. This half-toning method is defined as 3D ED (3D Error Diffusion).

Here, the first error diffusion unit according to an embodiment of the present invention will be described in detail with reference to FIGS. 17 to 18.

17 is a block diagram illustrating a first error diffusion method according to an embodiment of the present invention. 18 is a schematic diagram illustrating a first error diffusion method according to an embodiment of the present invention.

As shown in FIG. 18, the first error diffusion unit 1700 discards an error generated when the pixel is quantized for the least significant digit from the decimal point to a predetermined bit, thereby affecting neighboring pixels. Solves the error correction spatially. Here, the first error diffusion multiplies the error generated in the neighboring pixels a, b, c, and d by a specific coefficient, adds the added value to the i value, performs quantization, and stores the error generated in the line memory 1710 again. This is repeated every pixel. In addition, when the gradation value difference between adjacent pixels is large, the first error diffusion is performed by comparing with a predetermined threshold value as shown in FIG. 17.

As shown in FIG. 17, the first error spreader 1700 according to an embodiment of the present invention includes a line memory unit 1710, a first error diffusion determiner 1720, and a first error spreader 1730. ).

The line memory unit 1710 stores the inverse gamma corrected image signal in units of lines. In addition, the line memory unit 1710 stores the gray value of the image signal in which the first error diffusion is performed, and repeats it every pixel.

The first error diffusion determining unit 1720 compares the difference between the gray level values of the image signal stored in the line memory unit 1710 and the image signal of the adjacent pixel, and the difference in the gray level among the image signals of the adjacent pixel is equal to or less than a predetermined threshold value. Select the video signal of the pixel.

That is, the first error diffusion of the pixel in which the absolute value of the difference in the gray value of the video signal is equal to or less than the predetermined threshold value is selectively performed. At this time, the predetermined threshold is 1. Although the predetermined threshold value is set to 1 according to an embodiment of the present invention, it may be arbitrarily set according to the image to be implemented.

Determination of error diffusion according to an embodiment of the present invention is made for each pixel. That is, this is performed for all pixels during one frame in pixel units.

The first error spreading unit 1730 performs error component diffusion of an image signal of a pixel having a predetermined threshold value or less. As a result, it is possible to exclude adjacent pixels adversely affected by the error diffusion and to perform more reliable error diffusion.

In addition, the present invention performs the first error diffusion method for restraining from the flicker as shown in FIG. 20 is a schematic diagram illustrating a first error diffusion method according to an embodiment of the present invention.

As shown in FIG. 20, it is possible to use a ZigZag method in which directions are reversed for each line. In the conventional case, the video signal is applied to the panel in only one direction, and thus the error diffusion correction is performed in one direction. As a result, a worm artifact such as streaks appears on the screen and the screen is not clear. have.

Therefore, when the error diffusion in the zigzag method as described above it is possible to prevent the worm artifacts (worm artifact) problem that is a problem in the conventional Floyd steinberg method.

In addition, the second error diffusion unit according to an embodiment of the present invention will be described in detail as follows.

As shown in FIG. 21, the second error diffusion unit 2100 according to an embodiment of the present invention may include a frame memory unit 2110, a second error diffusion determination unit 2120, and a second error diffusion execution unit 2130. ).

The frame memory unit 2110 stores the inverse gamma corrected image signal in units of lines. In addition, the frame memory unit 2110 stores the gray scale value of the image signal in which the error diffusion is performed, and repeats it every pixel. In an exemplary embodiment of the present invention, the frame memory unit 2110 is included in the second error diffusion unit 2100, but a frame memory unit included in the plasma display panel may be used. That is, the frame memory unit may be located outside the second error diffusion unit.

The second error spreading determination unit 2120 obtains a difference between gray level values of the image signal of the previous frame N-1 input from the frame memory unit 2110 and the image signal of the current frame N input after inverse gamma correction. . Thereafter, the difference value of the grayscale value and a predetermined threshold value are compared to determine whether the error is spread.

The second error spreading unit 2130 spreads the error component of the image signal in time according to the information input from the second error diffusion determining unit 2120.

In an embodiment of the present invention, the gray level values of the image signals of the previous frame and the current frame are compared with each pixel, and error diffusion is performed.

At this time, error components of the video signal of the error-spread current frame are accumulated. That is, the error component of the previous frame N-1 is received from the current frame N to affect the current frame, and the error of the current frame is accumulated. By accumulating the error of the current frame affects the next frame (N + 1) again, it is possible to suppress the loss of the gradation representation due to the quantization of the image signal. Here, the difference between the gray level value of each of the previous frame, the current frame, the current frame, and the next frame must satisfy a predetermined threshold value or less.

When the difference in the gray value of the image signal according to the embodiment of the present invention exceeds a predetermined threshold value, the accumulated error component is erased. That is, since the human eye accumulates light in time and feels its brightness, when the gray value difference of the image signal exceeds a predetermined threshold value, spreading an error component adversely affects an image to be realized. Therefore, in an exemplary embodiment of the present invention, when the gray value difference of the image signal exceeds a predetermined threshold value, the accumulated error component is erased so that the gray value of the frame where the gray value difference occurs does not be affected.

At this time, the predetermined threshold value according to an embodiment of the present invention is characterized in that 1. Although the predetermined threshold value is set to 1 according to an embodiment of the present invention, it may be arbitrarily set according to the image to be implemented. After inverse gamma correction, the video signal has a gray value having an integer part and a fractional part. Accordingly, the image signal having a difference in gradation value of 1 or more does not perform error diffusion by a threshold value, and the image signal having a difference in gradation value of 1 or less performs error diffusion by a threshold value.

As a result, it is possible to exclude a video signal of a frame having an adverse effect due to the error spreading, to perform a more reliable error spreading, and to prevent the occurrence of flicker when only the temporal error spreading is performed.

The image processing method of the plasma display panel according to the exemplary embodiment of the present invention includes the following steps.

First, gamma correction is performed on an externally applied video signal with gamma data stored in advance.

Thereafter, the error component of the video signal of the adjacent pixel is spatially spread to the first error from the least significant digit to the predetermined bit of the inverse gamma corrected video signal.

Then, when the difference between the gray level value of the previous frame N-1 and the current frame N of the inverse gamma corrected video signal for bits below the decimal point other than the predetermined bit is less than or equal to the predetermined threshold value, the video signal of the previous frame. The second error spreading component of the error is temporally spread over the video signal of the current frame.

Thereafter, the image signal input after the second error diffusion step is mapped to the subfield mapping table.

At this time, the first error diffusion method is as shown in FIG. 19 is a schematic diagram illustrating a first error diffusion according to an embodiment of the present invention.

As shown in FIG. 19, an error diffusion block diagram is repeatedly performed through a spatial feedback routine so that an error correction value that is always output is mapped and output to a luminance value closest to the target luminance. In addition, the operation of the block diagram may be represented by Equations 1 and 2 below.

[Equation 1]

[Equation 2]

19 and the parameters of Equations 1 and 2 are defined as follows.

-n indicates the current frame.

-F (i, j) is a gray scale value input after the inverse gamma correction.

The -Q block is a quantization block.

-B (i, j) is the quantized grayscale value.

-E (i, j) is the error that occurs in quantization

-f (i, j) is a value obtained by adding a quantization error value to a gray scale value input after inverse gamma correction.

That is, f (i, j) is a value obtained by multiplying F (i, j) in the current frame by multiplying an error value of a pixel neighboring in the current frame by an error diffusion coefficient h (i, j) in H block. Therefore, the correction for the error is performed spatially.

In addition, the second error diffusion method is as shown in FIG. 22 is a schematic diagram illustrating a second error spreading according to an embodiment of the present invention.

The operation of the block of FIG. 22 may be represented by Equations 1, 2, and 3 below.

[Equation 1]

[Equation 2]

[Equation 3]

22 and the parameters of Equation 1, Equation 2 and Equation 3 are defined as follows.

D is an error diffusion determining block that determines whether or not an error is spread.

Q is a quantization block that quantizes the inverse gamma corrected video signal.

Z is an error component delay block that delays the error components in time.

n represents the current frame.

n-1 represents the previous frame.

F (i, j) represents the input image signal after inverse gamma correction. In this case, i and j are coordinates representing pixel positions of the video signal.

B (i, j) is a video signal quantized by a Q block.

E (i, j) is the temporal error component of the video signal. That is, the quantization error component generated in the previous frame.

f (i, j) is the error spread video signal. That is, f (i, j) is an image signal obtained by accumulating an error component delayed by one frame through Z blocks in the previous frame to F (i, j) in the current frame.

Referring to FIG. 22 and Equation 1, Equation 2, and Equation 3, first, the error diffusion is performed by comparing the difference of gray values with a predetermined threshold value and determining whether the error is spread. In FIG. 22, it is determined whether an error spreads in a D block.

At this time, in one embodiment of the present invention, when the difference between the grayscale value of the previous frame and the current frame is less than or equal to a predetermined threshold value, error diffusion is performed so that the f (i, j) value has the value shown in Equation (2).

In addition, when the difference between the gray level value of the previous frame and the current frame exceeds a predetermined threshold value, the error component is erased and initialized, so that the value of f (i, j) output from the D block is F (i , j).

As described above, by using the first error diffusion and the second error diffusion at the same time to perform error diffusion in time and space, the gray scale expression power can be increased, and flicker generated during error diffusion can be prevented.

Fourth Embodiment

FIG. 23 is a diagram illustrating a method of expressing grayscale using first error diffusion and second error diffusion according to an embodiment of the present invention. As shown in FIG. 15, a value above the decimal point of the gray scale is called a real gray scale, and temporal error diffusion and spatial error diffusion are used using a value below the decimal point. The first error diffusion is used temporally for the least significant digits after the decimal point and the predetermined bit, and the second error diffusion is spatially used for the decimal points other than the above-described predetermined bits. Herein, the predetermined bit is preferably 2 to 5 bits among the bits below the decimal point. In more detail, it is preferable that it is 4 bits of the decimal point bits. First, a carry occurs in the first error spreading bits (4 to 7 bits) and is transferred to the second error spreading bits (1 to 3 bits), and a carry occurs in the second error spreading bits to generate a real. Passed as (real) gradation bits. As a result, various gradation expressions are possible using only real gradation values. Here, the carry means a lift. Herein, the predetermined bits are shown as four bits, which are arbitrarily written to facilitate the description of the present invention, and are not limited thereto.

Here, an image processing apparatus of a plasma display panel that embodies gradation representation using first error diffusion and second error diffusion according to an embodiment of the present invention will be described with reference to FIG. 24.

24 is a block diagram schematically illustrating an image processing apparatus of a plasma display panel according to an embodiment of the present invention.

As illustrated in FIG. 24, an image processing apparatus of a plasma display panel according to an exemplary embodiment of the present invention may include an inverse gamma correction unit 2410, a gain control unit 2420, a first error diffusion unit 2431, and a second error. The diffusion unit 2432, the subfield mapping unit 2440, the data alignment unit 2450, and the data driver 2460 are provided.

The inverse gamma correction unit 2410 gamma-corrects an input image signal through pre-stored gamma data, and linearly converts a displayed luminance value according to a gray value of the input image signal.

The gain controller 2420 may be adjusted by a user or a set maker with respect to the red, green, and blue image signals corrected by the inverse gamma correction unit 2410. Adjust the gain by red, green and blue by multiplying the gain values. In this case, the gain controller 2420 may set a color temperature desired by the user or the set maker. In one embodiment of the present invention further includes a gain control unit 2420 for performing such a function.

The first error diffusion unit 2431 may diffuse the error component in time with respect to the image signal input from the gain control unit 2420, thereby finely adjusting the luminance value displayed according to the gray scale value to improve the gray scale expression power.

In performing the error diffusion, the first error spreader 2431 according to an embodiment of the present invention includes the previous frame (N-1) of the image signal inversely gamma corrected from the least significant digit to the predetermined bit after the decimal point. When the difference between the gray level value of the current frame and the current frame N is less than or equal to a predetermined threshold, temporal error spreading is performed to spread the error component of the image signal of the previous frame to the image signal of the current frame. The description thereof will be described later in more detail.

The second error diffusion unit 2432 spatially diffuses an error component into adjacent pixels with respect to an image signal input from the gain control unit 2420 with respect to a decimal point other than a predetermined bit, thereby displaying a luminance value displayed according to a gray scale value. By finely adjusting the gradation expression can be improved. In addition, the second error diffusion unit 2432 according to an embodiment of the present invention may perform error diffusion such that the difference between the grayscale values and the inverse gamma corrected image signal is less than or equal to a predetermined threshold. The error component of the video signal is spread. That is, it is possible to determine whether or not the error diffusion is performed according to the grayscale value of the adjacent pixel, and selectively perform the error diffusion. The description thereof will be described later in more detail.

The subfield mapping unit 2440 maps the image signal input from the second error diffusion unit 2432 to a preset subfield mapping table.

The data arranging unit 2450 sorts the spatially aligned subfield mapping data input from the subfield mapping unit 2440 into temporal data.

The data driver 2460 receives the data aligned in time by the data aligning unit 2450 and supplies an address driving pulse to an address electrode (not shown) of the plasma display panel, thereby realizing an image of the plasma display panel. This half-toning method is defined as 3D ED (3D Error Diffusion).

Here, the first error diffusion unit according to an embodiment of the present invention will be described in detail with reference to FIG. 29. As shown in FIG. 29, the first error spreading unit 2900 according to an embodiment of the present invention may include a frame memory unit 2910, a second error diffusion determination unit 2920, and a second error diffusion execution unit 2930. ).

The frame memory unit 2910 stores the inverse gamma corrected image signal in units of lines. In addition, the frame memory unit 2910 re-stores the gray value of the image signal in which the error diffusion is performed, and repeats it every pixel. In an exemplary embodiment of the present invention, the frame memory unit 2910 is included in the first error diffusion unit 2900, but a frame memory unit included in the plasma display panel may be used. That is, the frame memory unit may be located outside the first error diffusion unit.

The first error spreading determination unit 2920 obtains a difference between gray level values of the image signal of the previous frame N-1 input from the frame memory unit 2910 and the image signal of the current frame N input after the inverse gamma correction. . Thereafter, the difference value of the grayscale value and a predetermined threshold value are compared to determine whether the error is spread.

The first error spreading unit 2930 spreads the error component of the image signal in time according to the information input from the first error diffusion determining unit 2920.

In an embodiment of the present invention, the gray level values of the image signals of the previous frame and the current frame are compared with each pixel, and error diffusion is performed.

At this time, error components of the video signal of the error-spread current frame are accumulated. That is, the error component of the previous frame N-1 is received from the current frame N to affect the current frame, and the error of the current frame is accumulated. By accumulating the error of the current frame affects the next frame (N + 1) again, it is possible to suppress the loss of the gradation representation due to the quantization of the image signal. Here, the difference between the gray level value of each of the previous frame, the current frame, the current frame, and the next frame must satisfy a predetermined threshold value or less.

When the difference in the gray value of the image signal according to the embodiment of the present invention exceeds a predetermined threshold value, the accumulated error component is erased. That is, since the human eye accumulates light in time and feels its brightness, when the gray level difference of the image signal exceeds a predetermined threshold value, spreading an error component adversely affects the implemented image. Therefore, in an exemplary embodiment of the present invention, when the gray value difference of the image signal exceeds a predetermined threshold value, the accumulated error component is erased so that the gray value of the frame where the gray value difference occurs does not be affected.

At this time, the predetermined threshold value according to an embodiment of the present invention is characterized in that 1. Although the predetermined threshold value is set to 1 according to an embodiment of the present invention, it may be arbitrarily set according to the image to be implemented. After inverse gamma correction, the video signal has a gray value having an integer part and a fractional part. Accordingly, the image signal having a difference in gradation value of 1 or more does not perform error diffusion by a threshold value, and the image signal having a difference in gradation value of 1 or less performs error diffusion by a threshold value.

In addition, the second error diffusion unit according to an embodiment of the present invention will be described in detail with reference to FIGS. 25 to 26.

25 is a block diagram illustrating an operating characteristic of a second error spreader according to an embodiment of the present invention. 26 is a schematic diagram illustrating a second error diffusion method according to an embodiment of the present invention.

As illustrated in FIG. 26, as illustrated in FIG. 26, the second error spreader 2500 neighbors an error that occurs when the pixel is quantized with respect to the decimal point bits other than the above-described predetermined bits. By making an influence on the pixel to be solved, the correction for the discarded error is spatially solved. In this case, the first error diffusion multiplies the error generated in neighboring pixels a, b, c, and d by a specific coefficient, adds the added value to the i value, and quantizes and stores the error generated in the line memory 2510 again. This is repeated every pixel. In addition, when the gray value difference between adjacent pixels is large, the second error diffusion is performed as compared with a predetermined threshold value as shown in FIG. 25.

As shown in FIG. 25, the second error spreader 2500 according to an embodiment of the present invention includes a line memory unit 2510, a second error diffusion determiner 2520, and a second error spreader 2530. ).

The line memory unit 2510 stores the inverse gamma corrected image signal in line units. In addition, the line memory unit 2510 stores the gray value of the image signal in which the first error diffusion is performed, and repeats it for every pixel.

The second error spreading determination unit 2520 compares the difference in the gray level between the image signal stored in the line memory unit 2510 and the image signal of the adjacent pixel, and the difference in the gray level among the image signals of the adjacent pixel is equal to or less than a predetermined threshold value. Select the video signal of the pixel.

That is, the first error diffusion of the pixel in which the absolute value of the difference in the gray value of the video signal is equal to or less than the predetermined threshold value is selectively performed. At this time, the predetermined threshold is 1. Although the predetermined threshold value is set to 1 according to an embodiment of the present invention, it may be arbitrarily set according to the image to be implemented.

Determination of error diffusion according to an embodiment of the present invention is made for each pixel. That is, this is performed for all pixels during one frame in pixel units.

The second error spreading unit 2530 performs error component diffusion of an image signal of a pixel having a predetermined threshold value or less. As a result, it is possible to exclude adjacent pixels adversely affected by the error diffusion and to perform more reliable error diffusion.

In addition, the present invention performs a second error diffusion method for not being restricted by the flicker as shown in FIG. 28 is a schematic diagram illustrating a second error diffusion method according to an embodiment of the present invention.

As shown in FIG. 28, it is possible to use a ZigZag method in which the direction is reversed for each line. In the conventional case, the video signal is applied to the panel in one direction only, and the error diffusion correction is performed in one direction only. As a result, worm artifacts such as streaks appear on the screen and the screen is not clear. there is a problem.

Therefore, when the error diffusion in the zigzag method as described above it is possible to prevent the worm artifacts (worm artifact) problem that is a problem in the conventional Floyd steinberg method.

As a result, it is possible to exclude a video signal of a frame having an adverse effect due to the error spreading, to perform a more reliable error spreading, and to prevent the occurrence of flicker when only the temporal error spreading is performed.

The image processing method of the plasma display panel according to the exemplary embodiment of the present invention includes the following steps.

First, gamma correction is performed on an externally applied video signal with gamma data stored in advance.

Subsequently, when the difference between the grayscale values of the previous frame N-1 and the current frame N of the inverse gamma corrected video signal is less than or equal to a predetermined threshold value, the image of the previous frame with respect to the least significant digit from the decimal point to a predetermined bit. The error component of the signal is first spread in time to the video signal of the current frame.

Thereafter, an error component of an image signal of an adjacent pixel is spatially diffused to the second decimal point for bits below the decimal point other than the predetermined bit among the inverse gamma corrected image signals.

Thereafter, the image signal input after the second error diffusion step is mapped to the subfield mapping table.

At this time, the first error diffusion method is as shown in FIG. 30 is a schematic diagram illustrating a first error spreading according to an embodiment of the present invention.

The operation of the block of FIG. 30 may be represented by Equations 1, 2, and 3 below.

[Equation 1]

[Equation 2]

[Equation 3]

30 and the parameters of Equations 1, 2 and 3 are defined as follows.

D is an error diffusion determining block that determines whether or not an error is spread.

Q is a quantization block that quantizes the inverse gamma corrected video signal.

Z is an error component delay block that delays the error components in time.

n represents the current frame.

n-1 represents the previous frame.

F (i, j) represents the input image signal after inverse gamma correction. In this case, i and j are coordinates representing pixel positions of the video signal.

B (i, j) is a video signal quantized by a Q block.

E (i, j) is the temporal error component of the video signal. That is, the quantization error component generated in the previous frame.

f (i, j) is the error spread video signal. That is, f (i, j) is an image signal obtained by accumulating an error component delayed by one frame through Z blocks in the previous frame to F (i, j) in the current frame.

Referring to FIG. 30 and Equation 1, Equation 2, and Equation 3, first, the error diffusion is performed by comparing the difference of gray values with a predetermined threshold value and determining whether or not the error spreads. In FIG. 30, it is determined whether an error is spread in the D block.

At this time, in one embodiment of the present invention, when the difference between the grayscale value of the previous frame and the current frame is less than or equal to a predetermined threshold value, error diffusion is performed so that the f (i, j) value has the value shown in Equation (2).

In addition, when the difference between the gray level value of the previous frame and the current frame exceeds a predetermined threshold value, the error component is erased and initialized, so that the value of f (i, j) output from the D block is F (i , j).

In addition, the second error diffusion method is as shown in FIG. 27. 27 is a schematic diagram illustrating a second error spreading according to an embodiment of the present invention.

As shown in FIG. 27, an error diffusion block diagram is repeatedly performed through a spatial feedback routine so that an error correction value that is always output is mapped and output to a luminance value closest to the target luminance. In addition, the operation of the block diagram may be represented by Equations 1 and 2 below.

[Equation 1]

[Equation 2]

19 and the parameters of Equations 1 and 2 are defined as follows.

-n indicates the current frame.

-F (i, j) is a gray scale value input after the inverse gamma correction.

The -Q block is a quantization block.

-B (i, j) is the quantized grayscale value.

-E (i, j) is the error that occurs in quantization

-f (i, j) is a value obtained by adding a quantization error value to a gray scale value input after inverse gamma correction.

That is, f (i, j) is a value obtained by multiplying F (i, j) in the current frame by multiplying an error value of a pixel neighboring in the current frame by an error diffusion coefficient h (i, j) in H block. Therefore, the correction for the error is performed spatially.

As such, by using the first error diffusion and the second error diffusion at the same time to perform error diffusion in time and space, the gray scale expression power can be increased, and flicker generated during error diffusion can be prevented.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains can understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential features. will be. Therefore, the above-described embodiments are to be understood as illustrative and not restrictive in all respects, and the scope of the present invention is indicated by the appended claims rather than the detailed description, and the meaning and scope of the claims and All changes or modifications derived from the equivalent concept should be interpreted as being included in the scope of the present invention.

The image processing apparatus of the plasma display panel according to the exemplary embodiment of the present invention configured as described above can increase gray scale expressive power, and can prevent flicker generated during error diffusion.

Claims (22)

An inverse gamma correction unit configured to gamma correct an image signal applied from the outside with gamma data stored in advance; A dither half toning unit which removes the pseudo contour generated in the inverse gamma correction step from a plurality of dither mask patterns with respect to the least significant digit from the decimal point to a predetermined bit; When the difference between the gray level value of the previous frame N-1 and the current frame N of the inverse gamma corrected video signal is less than or equal to a predetermined threshold value for a bit less than the decimal point other than the predetermined bit, the image signal of the previous frame An error diffusion unit for diffusing an error component into the video signal of the current frame; And Subfield mapping unit for mapping the video signal input from the error diffusion unit to the subfield mapping table An image processing apparatus of a plasma display panel comprising a. The method of claim 1, And the predetermined bit is 2 to 5 bits of a decimal point bit. The method of claim 1, The error diffusion unit A frame memory unit for storing the inverse gamma corrected image signal in units of frames; An error diffusion determining unit which determines whether or not an error is spread by comparing a difference between gray levels of a previous frame and a current frame of the image signal with the predetermined threshold value; And An error diffusion unit for diffusing an error component of an image signal according to the information input from the error diffusion determination unit An image processing apparatus of a plasma display panel comprising a. The method according to claim 1 or 3, And said predetermined threshold value is one. An inverse gamma correction unit configured to gamma correct an image signal applied from the outside with gamma data stored in advance; When the difference between the grayscale values of the previous frame N-1 and the current frame N of the inverse gamma corrected video signal is less than or equal to a predetermined threshold value, the video signal of the previous frame with respect to the least significant digit from the decimal point to a predetermined bit. An error diffusion unit configured to diffuse an error component of the current signal into the video signal of the current frame; A dither half toning unit which removes pseudo contours generated in the inverse gamma correction step using a plurality of dither mask patterns with respect to the decimal point bits other than the predetermined bits; And Subfield mapping unit for mapping the video signal input from the dither half toning unit to the subfield mapping table An image processing apparatus of a plasma display panel comprising a. The method of claim 5, And the predetermined bit is 2 to 5 bits of a decimal point bit. The method of claim 5, The error diffusion unit A frame memory unit for storing the inverse gamma corrected image signal in units of frames; An error diffusion determining unit which determines whether or not an error is spread by comparing a difference between gray levels of a previous frame and a current frame of the image signal with the predetermined threshold value; And An error diffusion unit for diffusing an error component of an image signal according to the information input from the error diffusion determination unit An image processing apparatus of the plasma display panel comprising a. The method according to claim 5 or 7, And said predetermined threshold value is one. An inverse gamma correction unit configured to gamma correct an image signal applied from the outside with gamma data stored in advance; A first error diffusion unit configured to diffuse an error component of an image signal of an adjacent pixel from a least significant digit to a predetermined bit among the inverse gamma corrected image signals; When the difference between the gray level value of the previous frame N-1 and the current frame N of the inverse gamma corrected video signal is less than or equal to a predetermined threshold value for a bit less than the decimal point other than the predetermined bit, the image signal of the previous frame A second error spreader for diffusing an error component into the video signal of the current frame; And A subfield mapping unit for mapping an image signal input from the second error spreading unit to a subfield mapping table An image processing apparatus of a plasma display panel comprising a. The method of claim 9, And the predetermined bit is 2 to 5 bits of a decimal point bit. The method of claim 9, The first error diffusion unit A line memory unit for storing the inverse gamma corrected image signal in line units; A first error diffusion for comparing a difference in gray level between the image signal stored in the line memory unit and an image signal of an adjacent pixel, and selecting an image signal of a pixel whose difference in the gray level is less than or equal to a predetermined threshold value among the image signals of the adjacent pixel; Determination unit; And A first error spreading unit performing diffusion of error components of the image signal of the selected pixel An image processing apparatus of a plasma display panel comprising a. The method according to claim 9 or 11, And said predetermined threshold value is one. The method according to claim 9 or 11, The first error spread is An image processing apparatus of a plasma display panel, wherein directions are reversed for each line. The method of claim 9, The second error diffusion unit A frame memory unit for storing the inverse gamma corrected image signal in units of frames; A second error spreading determination unit which determines whether or not an error is spread by comparing a difference between gray levels of a previous frame and a current frame of the image signal with the predetermined threshold value; And A second error diffusion unit configured to diffuse an error component of an image signal according to information input from the second error diffusion determination unit An image processing apparatus of a plasma display panel comprising a.        The method according to claim 9 or 14, And said predetermined threshold value is one.        An inverse gamma correction unit configured to gamma correct an image signal applied from the outside with gamma data stored in advance;        When the difference between the grayscale values of the previous frame N-1 and the current frame N of the inverse gamma corrected video signal is less than or equal to a predetermined threshold value, the video signal of the previous frame with respect to the least significant digit from the decimal point to a predetermined bit. A first error spreader which spreads an error component of the current signal to the video signal of the current frame;        A second error diffusion unit configured to diffuse an error component of an image signal of an adjacent pixel to bits below the decimal point other than the predetermined bit among the inverse gamma corrected image signals; And        A subfield mapping unit for mapping an image signal input from the second error spreading unit to a subfield mapping table        An image processing apparatus of a plasma display panel comprising a.        The method of claim 16, And the predetermined bit is 2 to 5 bits of a decimal point bit.        The method of claim 16,        The second error diffusion unit        A line memory unit for storing the inverse gamma corrected image signal in line units; A second error diffusion for comparing the difference in gray level between the image signal stored in the line memory unit and the image signal of the adjacent pixel, and selecting an image signal of the pixel whose difference in the gray level is less than or equal to a predetermined threshold value among the image signals of the adjacent pixel; Determination unit; And A second error spreading unit performing diffusion of error components of the image signal of the selected pixel An image processing apparatus of a plasma display panel comprising a. The method of claim 16 or 18, And said predetermined threshold value is one. The method of claim 16 or 18, The second error spread is An image processing apparatus of a plasma display panel, wherein directions are reversed for each line. The method of claim 16, The first error diffusion unit A frame memory unit for storing the inverse gamma corrected image signal in units of frames;       A first error spreading determination unit which determines whether or not an error is spread by comparing a difference between grayscale values of the previous frame and the current frame of the video signal with the predetermined threshold value; And       According to the information input from the first error diffusion determination unit, the error component of the image signal is first error diffusion unit; An image processing apparatus of a plasma display panel comprising a. The method of claim 16 or 21, And said predetermined threshold value is one.

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